Dielectric materials for power transfer system

ABSTRACT

A contactless power transfer system is proposed. The power transfer system comprises a field-focusing element comprising a dielectric material. The dielectric material comprises a composition that is selected from the family of (Ba,Sr)TiO 3  or CaCu 3 Ti 4 O 12 . The compositions of the (Ba,Sr)TiO 3  include the materials such as Ca 1-x-y Ba x Sr y Ti 1-z Cr z O 3-δ N p , wherein 0&lt;x&lt;1; 0&lt;y&lt;1; 0≦z≦0.01; 0≦δ≦1; and 0≦p≦1. The compositions of the CaCu 3 Ti 4 O 12  include the materials such as Ca 1-x-y Ba x Sr y  (Ca 1-z Cu z )Cu 2 Ti 4-δ Al δ O 12-0.5δ , wherein 0≦x&lt;0.5; 0≦y&lt;0.5; 0≦z≦1; and 0≦δ≦0.1.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. patent application,Docket Number 238312-1, Ser. No. ______, entitled “DIELECTRIC MATERIALSFOR POWER TRANSFER SYSTEM” filed contemporaneously herewith, whichapplication is hereby incorporated by reference.

BACKGROUND

The invention relates generally to power transfer systems, and, inparticular, to resonance based contactless power transfer systems.

In certain applications where instantaneous or continuous energytransfer is needed but interconnecting wires are inconvenient,contactless power transfer is desirable. One contactless power transfermethod is an electromagnetic induction method that works on theprinciple of a primary transformer coil generating a dominant magneticfield and a secondary transformer coil in the vicinity of the primarytransformer coil generating a corresponding voltage. The magnetic fieldreceived by the secondary transformer coil decreases as a function ofthe square of the distance between the two coils, and hence the couplingbetween primary and secondary coils is weak for distances greater than afew millimeters.

Another method of contactless power transfer attempts to increase theefficiency of the inductive power transfer by resonant inductivecoupling. Transmitter and receiver elements resonate at the samefrequency, and maximum induction occurs at the resonant frequency.However, such resonant induction is sensitive to load and gapvariations.

There is a need for an efficient contactless power transfer system thatmay operate with coils separated by longer distances than are presentlyacceptable and is efficient when subjected to misalignment or loadvariations. Further, there is a need for accommodating and efficientmaterials, having high dielectric properties and low dielectric lossfactors, that can be used in the power transfer systems in the requiredfrequency ranges.

BRIEF DESCRIPTION

Briefly, in one embodiment, a power transfer system is provided. Thepower transfer system comprises a field-focusing element comprising adielectric material. The dielectric material comprises a compositionwith the formula Ca_(1-x-y)Ba_(x)Sr_(y)Ti_(1-z)Cr_(z)O_(3-δ)N_(p),wherein x and y can vary between the value of zero and one such that0<x<1 and 0<y<1; z can vary between the value of zero and 0.01 such that0≦z≦0.01; and δ and p can vary between the value of zero and one suchthat 0≦δ≦1 and 0≦p≦1.

In one embodiment, a power transfer system is provided. The powertransfer system comprises a first coil coupled to a power source and asecond coil coupled to a load; and a field-focusing element comprising adielectric material and disposed between the first coil and the secondcoil. The dielectric material comprises a composition with the formulaCa_(1-x-y)Ba_(x)Sr_(y)Ti_(1-z)Cr_(z)O_(3-δ)N_(p), wherein x and y canvary between the value of zero and one such that 0<x<1 and 0<y<1; z canvary between the value of zero and 0.01 such that 0≦z≦0.01; and δ and pcan vary between the value of zero and 0.5 such that 0≦δ≦0.5 and0≦p≦0.5.

In another embodiment, a power transfer system is provided. The powertransfer system comprises a field-focusing element comprising adielectric material. The dielectric material comprisesCa_(1-x-y)Ba_(x)Sr_(y)(Ca_(1-z)Cu_(z))Cu₂Ti_(4-δ)Al_(δ)O_(12-0.5δ),wherein x and y can vary between the value of zero and 0.5 such that0≦x<0.5 and 0≦y<0.5, z can vary between the value of zero and one suchthat 0≦z≦1; and δ can vary between the value of zero and 0.1 such that0≦δ≦0.1.

In one embodiment, a power transfer system is provided. The powertransfer system comprises a first coil coupled to a power source and, asecond coil coupled to a load, and a field-focusing element disposedbetween the first coil and the second coil. The field-focusing elementcomprises a dielectric material such that the dielectric materialcomprises Ca_(1-x-y)Ba_(x)Sr_(y)Cu₃Ti₄O₁₂, wherein x and y can varybetween the value of zero and 0.2 such that 0<x<0.2 and 0<y<0.2.

In one embodiment, a power transfer system is provided. The powertransfer system comprises a first coil coupled to a power source, asecond coil coupled to a load, and a field-focusing element disposedbetween the first coil and the second coil. The field-focusing elementcomprises a dielectric material, wherein the dielectric materialcomprises Ca_(2-x-y)Ba_(x)Sr_(y)Cu₂Ti_(4-δ)Al_(δ)O_(12-0.5δ), wherein xand y can vary between the value of zero and 0.2 such that 0≦x<0.2 and0≦y<0.2 and δ can vary between the value of zero and 0.1 such that0<δ≦1.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates an exemplary contactless power transfer systemaccording to an embodiment of the invention;

FIG. 2 illustrates an exemplary field-focusing element according to anembodiment of the invention;

FIG. 3 illustrates multiple exemplary structures of field-focusingelements according to various embodiments of the invention;

FIG. 4 illustrates an embodiment wherein a plurality of resonators arearranged in an array and implemented as a field-focusing element; and

FIG. 5 illustrates multiple exemplary structures of embedding materialsaccording to an embodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention include power transfer systems andthe dielectric materials that can be used for the power transfersystems.

In the following specification and the claims that follow, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly dictates otherwise.

Contactless power transfer systems are typically characterized by shortdistance power transfer between primary and secondary coils. Forexample, one embodiment of an inductive power transfer system uses aprimary coil and a secondary coil to transfer power between two circuitsin galvanic isolation. A magnetic field is established around theprimary coil when coupled to a power source. The quantity of powertransferred from the primary coil to the secondary coil is proportionalto the level of primary magnetic field linking the secondary coil.Electrical transformers use high permeability magnetic cores to link themagnetic field between primary and secondary coils and thus achieveefficiencies on the order of at least about 98%. However, when suchsystems are configured for contactless power transfer, the air gapbetween the two coils reduces the magnetic field coupling. Such reducedcoupling affects efficiency of contactless power transfer systems.

Certain embodiments disclosed herein provide a robust contactless powertransfer system with reduced sensitivity to load variations, efficientpower transfer during misalignment of coils, and a field-focusingstructure that enhances power transfer efficiency.

FIG. 1 illustrates an example of a contactless power transfer system 10according to an embodiment of the invention including a first coil 12coupled to a power source 14 and configured to produce a magnetic field(not shown). A second coil 16 is configured to receive power from thefirst coil 12. As used herein, the term “first coil” may also bereferred to as a “primary coil,” and the term “second coil” may also bereferred to as a “secondary coil.” The primary and secondary coils canbe made up of any good electrical conducting materials such as, forexample, copper. Field-focusing element 18 is disposed between the firstcoil 12 and the second coil 16 for focusing the magnetic field frompower source 14. In another embodiment, the field-focusing element maybe used to focus electric fields and/or electro-magnetic fields. Theterms “magnetic field-focusing element” and “field-focusing element” areused interchangeably. In one embodiment, magnetic field-focusing element18 is configured as a self-resonant coil and has a standing wave currentdistribution when excited via the first coil. In another embodiment, themagnetic field-focusing element includes multiple resonators operatingas an active array or a passive array and each resonator configured as aself-resonant coil with a standing wave current distribution. In yetanother embodiment, the magnetic field-focusing element includesmultiple sets of such resonators, each such resonator set excited at aparticular phase. It may be appreciated that, when exciting the sets ofresonators via different phases, field-focusing may be enhanced in adesired direction.

Magnetic field-focusing element 18 is further configured to focus themagnetic field onto the second coil 16 enhancing the coupling betweenthe first coil 12 and the second coil 16. In one embodiment, anon-uniform magnetic field distribution is developed around magneticfield-focusing element 18 by creating a standing wave currentdistribution in the field-focusing element 18. In the illustratedembodiment, field-focusing element 18 is placed closer to the first coil12 as an example. It may be advantageous in certain systems to place thefield-focusing element 18 closer to the second coil 16. A load 20 iscoupled to the second coil 16 to utilize the power transferred from thepower source 14. In certain embodiments, the contactless power transfersystem 10 may also be configured to simultaneously transfer power fromthe second coil to the first coil such that the system is capable ofbidirectional power transfer. Non-limiting examples of potential loadsinclude a bulb, a battery, a computer, a sensor, or any device thatrequires electrical power for operation.

The contactless power transfer system 10 may be used to transfer powerfrom the power source 14 to the load 20. In one embodiment, the powersource 14 comprises a single-phase AC power generator or three-phase ACpower generator in combination with power conversion electronics toconvert the AC power to a higher frequency. When the first coil 12 isexcited at the resonant frequency of magnetic field-focusing element 18,a standing wave current distribution is developed within the magneticfield-focusing element 18 between two open ends (22, 24) of thefield-focusing element. The standing wave current distribution leads toa non-uniform magnetic field distribution around magnetic field-focusingelement 18. Such non-uniform current distribution is configured to focusmagnetic field in any desired direction, such as, in a direction of thesecond coil 16 in this example. When operating at resonant frequency,even a small excitation to magnetic field-focusing element 18 produces alarge amplitude of current distribution along the length 25 of themagnetic field-focusing element. This large current magnitude ofnon-uniform distribution leads to an amplified and focused magneticfield in the direction of second coil 16 that results in higherefficiency of power transfer.

FIG. 2 illustrates an example of a field-focusing element according toan embodiment of the invention. Among the various structures that may beimplemented as the magnetic field-focusing element 18 in FIG. 1, onesuch structure is illustrated in FIG. 2. In the illustrated embodiment,the reference numeral 30 is a field-focusing structure herein referencedas an “Omega structure” and operates in a range of a few megahertz. The“Omega structure” enables high capacitance and inductance and alsoenables negative permeability at near resonant frequency. Negativepermeability helps with dominant field response and is effective incontrolling the magnetic field. Resonant frequency of such structurescan be controlled by varying the number of turns (32, 34, 36), the gapbetween the turns (38), and the width of the spiral (40). With anincreased perimeter as compared to a spiral structure, the “omegastructure” requires reduced structural size to operate at lowerresonance frequency.

FIG. 3 illustrates multiple examples of structures for field-focusingelements according to various embodiments of the invention. In oneembodiment, the field-focusing element includes a single loop coil 50.In another embodiment, the field-focusing element includes multipleturns such as in a split ring structure 52, spiral structure 54,Swiss-roll structure 56, or helical coil 58. Selection of a structurefor a particular application is determined by the size andself-resonating frequency of the field-focusing element. For example, inlow power applications (less than about 1 Watt, for example), aresonance frequency up to about 1000 MHz is feasible. In high powerapplications (from about one hundred Watts to about 500 kilowatts, forexample), the resonance frequency of the order of several hundred kHz isfeasible.

FIG. 4 illustrates an embodiment wherein a plurality of resonators arearranged in an array and implemented as a field-focusing element. Anarray of resonators constitutes multiple resonator coils arranged in aparticular array arrangement, such as a linear or planar array, that isexcited with a specific phase relationship. Individual resonators(66-77) or sub-wavelength resonators are configured to focus themagnetic field in a desired direction. In such an arrangement, fieldsfrom resonators in the array interfere constructively (add) in a desireddirection to achieve magnetic field-focusing and interfere destructively(cancel each other) in the remaining space. In another embodiment, theresonators are arranged in at least one of a linear, a circular, aplanar, or a three-dimensional array. In the illustrated embodiment,individual resonators 70-74 are arranged in a row and four such rows66-69 are arranged one below the other. Individual resonators that arepart of the array 64 are collectively configured for at least one ormore resonant frequencies. In a particular embodiment, all of theindividual resonators of the array are identical within the normal scopeof variation expected for manufacturing and other common sources ofvariation.

In one embodiment of the power transfer system of the present invention,the resonator of the field-focusing element 18 can be made of dielectricmaterials in the form of, for example, dielectric cavity resonators. Thedielectric materials used in field-focusing element desirably have highdielectric constant (dielectric permittivity, ∈) and low loss tangent.The high dielectric constant helps in achieving the low frequency ofresonance with given smaller dimensions of resonator while the low losstangent is desirable to keep the dielectric losses within acceptablelimits.

In one embodiment, the field-focusing element 18 comprises aself-resonant coil that focuses the magnetic field upon excitation atthe resonant frequency. The resonator is self-resonant coil of any shapewhose self-resonant frequency depends upon the self-capacitance andself-inductance. The self-resonant frequency of the coil is dependant onthe coil geometrical parameters. For example, in the case of helicalresonator coil, the resonance frequency is such that the overall lengthof the helix is half wavelength or multiples of half wavelength ofelectromagnetic excitation. As a result, design of these resonators atlow frequencies is challenging due to the space constraints. One of themethods to miniaturize the size of resonators is to embed the resonatorin a high dielectric constant medium.

In one embodiment, a resonator or an array of resonators of thefield-focusing element 18 is embedded in a material having highdielectric constant or a magnetic material having high permeability ormagneto-dielectric medium having high dielectric permittivity and highmagnetic permeability to achieve lower resonant frequency with a smallersized resonator. High permeability material enhances self-inductance ofthe resonator and high permittivity material enhances self-capacitanceof the resonators to reduce the frequency of resonance. In anotherembodiment, high permeability materials are also configured to increasethe coupling between the primary coil and the field-focusing element,and between the field-focusing element and the secondary coil. The highdielectric constant of the embedding material helps in decreasing theoperational frequency range of the resonators. The effect of dielectricconstant in the frequency reduction is presented in Table 1.

TABLE 1 Dielectric constant Frequency kHz 1 40600 1000 1380 10000 420100000 132

When the resonator is embedded in dielectric medium the inter-turncapacitance between the turns of the coil increases which in turn helpsto reduce the resonant frequency of the resonator. With high dielectricconstant, size reduction of the resonator is possible to a great extent.Another advantage of high dielectric constant is the confinement ofelectric field within the resonator, improving the efficiency of powertransfer as the radiation losses are diminished. But one of the criticaldesign criteria of the selection of material with high dielectricconstant is the loss tangent of that material at the operatingfrequency. The low dielectric loss tangent ensures the maximum couplingefficiency. If the loss tangent is high, the loss in the form of heatwill be high in the resonator. The issue of heat loss is of importancewhen the power levels are high. For low power levels, the high losstangent values are acceptable. A high dielectric constant and extremelylow loss tangent dielectric material is desirable in application wherethe power levels are more than one kW. The high dielectric constanthelps to achieve miniaturized resonators at frequencies of hundreds ofkHz and the low loss tangent helps to reduce the losses in thedielectric.

Power transfer systems enabled through high dielectric constant and lowloss tangent materials have applications including electric vehiclescharger, power transfer to rotating load, contactless charging of miningvehicles, where the power transfer levels are on the order of a few kW.Power transfer systems having high dielectric constant and high lossdielectric materials can be used in applications like subsea connectors,where the power levels are few milliwatts.

High dielectric constant materials with different shapes can act asfield-focusing elements. For example, a high dielectric constantcircular dielectric disc can act as a resonator at certain frequencies.The resonant frequency in this case is determined by the geometricalconfiguration of the resonator. Non limiting examples of the differentshapes of the resonators that can be used as field-focusing elements aregiven in FIG. 5. Field-focusing element 18 can be stacked as multi-layerresonators to yield multiple resonant frequencies. This kind ofconfiguration helps for multidirectional power transfer in which one ofthe channels can be used for power transfer and other channels can beused for low power data transmission between different devices.

The high dielectric constant material can also be used as a thin film orthick film coating on a metal surface to create field focusingstructures like swiss roll structure 56. The high dielectric constantbetween the different layers of the swiss roll increases the capacitanceof the structure and thereby reducing the frequency considerably.

Materials such as, but not limited to, calcium copper titanate andbarium strontium titanate are examples of materials exhibiting highdielectric constant. In one embodiment, the dielectric material is usedas a bulk material. The term “bulk material” as used herein indicatesany material that has a three dimensional structure with all of thesides greater than about 1 mm. In one embodiment, the dielectricmaterials are used as coatings. The coating can be in a thin film formor in a thick film form. As used herein a “thin film” has a thicknessless than about 100 microns, while a thick film can have thickness fromabout a hundred microns to about a millimeter.

In one embodiment, a combination of materials can be used for embeddingthe resonators. For example, a mixture of two or more materials havinghigh dielectric constant or two or more materials having highpermeability can be used as the embedding material. In anotherembodiment, a mixture of two or more materials, each having a highdielectric constant or a high permeability can be used as the embeddingmaterial.

Barium strontium titanate —(Ba,Sr)TiO₃— and calcium copper titanate—CaCu₃Ti₄O₁₂— have different crystal structures and exhibit differenttemperature dependent characteristics. For example, (Ba,Sr)TiO₃ belongsto a perovskite family and is a ferroelectric material with a cubic totetragonal crystal structure transition around the temperature of about120° C. CaCu₃Ti₄O₁₂ is not a ferroelectric material and has a bodycentered cubic (b.c.c) structure. The factors influencing the dielectricproperties such as dielectric constant and dielectric loss tangent inthe (Ba,Sr)TiO₃ and CaCu₃Ti₄O₁₂ systems may also be different. Forexample, it is believed that the generation and ordering of dipoles is areason for the ferroelectricity and the high dielectric constant in the(Ba,Sr)TiO₃ system, while the CaCu₃Ti₄O₁₂ system is thought to have theeffects arising from barrier layer capacitance by having insulatinggrain boundaries and semi conducting grains.

In one embodiment, it is desirable to use dielectric materials whosedielectric properties such as dielectric constant and loss tangent aresubstantially stable over a certain frequency range of the desiredapplications. The term “substantially stable” herein means that thechange in values does not lead to more than about 10% of the performancevariation of the power transfer system. Thus, the required value andwidth of the frequency ranges may vary depending on the applications forwhich the field-focusing element is used. In one embodiment, the desiredfrequency range is from about 100 Hz to about 100 MHz. In someembodiments, the desired frequency range is from about 1 kHz to about100 kHz. In another embodiment, the desired frequency range is fromabout 100 kHz to about 1 MHz. In one more embodiment, the desiredfrequency range is from about 1 MHZ to about 5 MHz.

Materials having a low dielectric loss tangent along with highdielectric constant will function efficiently in enhancing theself-capacitance of the resonators when used as the embedding materialsor cavity resonators, compared to materials that have low dielectricconstant and high loss tangent. Therefore, materials that have both highdielectric constant and low dielectric loss tangent at the frequency ofoperation of the resonators are desirable to be used in thefield-focusing element 18.

A dielectric material to be used in a field-focusing element 18 of thepower transfer system would generally require a high dielectric constantthat is equal to or greater than about 100 and a loss tangent that is aslow as possible. In one embodiment, a loss tangent equal to or less thanabout 0.1 may be acceptable for a dielectric material to be used infield-focusing element. In a subsequent embodiment, a loss tangent equalto or less than about 0.01 is desirable for the dielectric material.

The inventors studied different ways of improving the desirabledielectric properties of the dielectric materials belonging to the(Ba,Sr)TiO₃ and CaCu₃Ti₄O₁₂ systems. The different methods investigatedfor the property enhancements include, but are not limited to, cationdoping, anion doping, grain boundary doping, density increment,composite formations, and changing the sintering conditions, sinteringatmospheres, and structural and microstructural aspects.

Accordingly, in one embodiment, a material system with the formulaCa_(1-x-y)Ba_(x)Sr_(y)Ti_(1-z)Cr_(z)O_(3-δ)N_(p) wherein 0<x<1; 0<y<1;0≦z≦0.01; 0≦δ≦1; and 0≦p≦1 is provided for use in, for example, thefield-focusing element 18 of the power transfer system described above.This system will be henceforward referred to as “BST material system”for simplicity. As used herein, the term ‘greater than zero’ denotesthat the intended component is intentionally added, rather than anincidental amount that may be present as an impurity. As used herein,end points of the ranges include incidental variations above and belowthe stated number, as appropriate for normal measurement and processvariations. In one embodiment, a power transfer system is presentedcomprising BST material system as a dielectric material.

In one embodiment, a material system with the formulaCa_(1-x-y)Ba_(x)Sr_(y) (Ca_(1-z)Cu_(z))Cu₂Ti_(4-δ)Al_(δ)O_(12-0.5δ)wherein 0≦x<0.5, 0≦y<0.5; 0≦z≦1; and 0≦δ≦0.1 is presented for use in,for example, the field-focusing element 18 of the power transfer systemdescribed above. This system will be henceforward referred to as “CCTmaterial system” for simplicity. As used herein in the CCT materialsystem, the formulaCa_(1-x-y)Ba_(x)Sr_(y)(Ca_(1-z)Cu_(z))Cu₂Ti_(4-δ)Al_(δ)O_(12-0.5δ) is atheoretical formula including the mixtures and compounds that are in thespecified ratio to be denoted by this formula, and does not necessarilymean that a single compound exists in a form that can be identified bystandard characterization techniques. In short, a material specified bythe above formula may actually exist as multiple phases which, takencollectively, have an overall composition as specified by the formula.In one embodiment, a power transfer system is presented comprising CCTmaterial system as a dielectric material.

In general, the cation dopants were found to increase resistance of thegrain boundary by absorbing the oxygen vacancies and thereby decreaseboth the dielectric constant and loss tangent. By doping at the cationsite, the doped cation gets reduced by absorbing the electron density atthe grain boundary, thereby decreasing the conduction of the grainboundary, thus leading to the decrease in dielectric constant and loss.

In general, by doping at the anion site, the cation of the lattice getsreduced by absorbing the electron density thereby creating insulatingplanar defects in the grains. The insulating planar defects can reducethe electrical resistivity of internal barrier of the grains and therebydecrease the dielectric loss.

In the BST material system, the barium and strontium levels were variedand studied for their effects on favorable dielectric properties. Thus,in one embodiment, a power transfer system comprising a BST materialsystem is provided such that 0.3≦x. Therefore, in this embodiment, thebarium level is equal to or greater than about 0.3. In a furtherembodiment, x+y=1. Therefore, in this embodiment the BST material systemdoes not contain any other dopants in the barium or strontium sites. Inone embodiment, the strontium level in the BST material system is suchthat 0.4≦y<1. Therefore, in this embodiment, the strontium level isalways equal to or greater than about 0.4. Examples of the above BSTmaterial systems include, but are not limited to, Ba_(0.3)Sr_(0.7)TiO₃and Ba_(0.4)Sr_(0.6)TiO₃.

In one embodiment of the power transfer system with a BST materialsystem, the barium or strontium of the BST material system is partiallyreplaced by cations such as calcium to enhance favorable dielectricproperties. In one embodiment, a BST material system is such that0.9≦x+y<1. Thus, in this embodiment, the BST material system containsanother dopant in the barium or strontium sites, but the value of thedopant is always equal to or less than about 0.1. Examples of the aboveBST material systems include, but are not limited to,Ba_(0.55)Sr_(0.40)Ca_(0.05)TiO₃ and Ba_(0.5)Sr_(0.4)Ca_(0.1)TiO₃.

In one embodiment of the power transfer system with a BST materialsystem, the titanium is partially replaced by chromium, which may helpto decrease the loss tangent. In one embodiment, the chromium issubstituted for less than about 2 atomic % of titanium in the BSTmaterial system. In a subsequent embodiment, the chromium substitutionis in the range of about 0.01 atomic % to about 1 atomic %. Thus, inthis embodiment, the quantity z in the formula above varies betweenabout 0.0001 and about 0.01. In a further embodiment, the chromiumsubstitution is in the range of about 0.2 atomic % to about 1 atomic %of titanium with the z value varying between about 0.002 and about 0.01.In one embodiment, in a BST material system, z>0, and δ and p are bothequal to 0. In this embodiment, the BST material system comprises cationsubstitutions, but not anion substitutions. Examples of the above BSTmaterial systems include, but are not limited to,Ba_(0.3)Sr_(0.7)Cr_(0.002)Ti_(0.998)O₃. In a BST system, when titaniumis substituted with a trivalent cation, such as chromium in the aboveexample, the oxygen level can also stoichiometrically change. Forinstance in the above example, the number of oxygen atoms can be 2.999,instead of 3, to accommodate substitution of 0.002 atoms of chromium. Ina further embodiment, in the BST material system, the barium orstrontium is partially replaced by cations such as calcium or lanthanum;and titanium is partially replaced by chromium. Examples of the aboveBST material systems include, but are not limited to,Ba_(0.55)Sr_(0.4)Ca_(0.5)Cr_(0.002)Ti_(0.998)O₃. Table 2 belowrepresents some examples of the BST material systems and theirdielectric properties with the varying levels of barium and strontiumand with some cation dopants.

TABLE 2 Dielectric Loss BST material system Frequency constant tangentBa_(0.3)Sr_(0.7)TiO₃ 10 kHz-1 MHz >640 ~0.01 ~10 kHz ~645 ~0.006Ba_(0.4)Sr_(0.6)TiO₃ 10 kHz-10 MHz >480 <0.02 ~2.3 MHz >480 <0.0002Ba_(0.4)Sr_(0.6)Cr_(0.002)Ti_(0.998)O₃ 1 kHz-1 MHz >740 <0.09 ~339kHz >740 ~0.0004 Ba_(0.4)Sr_(0.6)Cr_(0.005)Ti_(0.995)O₃ 1 kHz-1 MHz >910<0.009 ~660 kHz >910 <0.0002

In one embodiment of the power transfer system with a BST materialsystem, the oxygen is partially replaced by nitrogen via anion doping.Nitrogen and fluorine are two examples of anion dopants used tosubstitute for oxygen. In one embodiment, the nitrogen is substitutedsuch that 0≦δ≦1; and 0≦p≦1 in the BST material system. Therefore, in oneembodiment, the anion substitution is such that about 25% or less ofoxygen in the BST material system is substituted by nitrogen. In oneembodiment, depending on the process conditions, the nitrogen is in anoxidation state of −3 while substituting for oxygen in the BST materialsystem. In one embodiment, the nitrogen is substituted such that 0≦δ≦1and 0≦p≦0.8. In one embodiment, the nitrogen substitution replaces lessthan about 10 atomic % of oxygen in the BST material system. In oneembodiment, the nitrogen is substituted such that 0.1≦δ≦0.8 and0.1≦p≦0.8. In one embodiment, the oxygen is substituted by fluorineinstead of nitrogen such that 0≦δ≦1; and p=0. In a further embodiment,the oxygen is substituted by fluorine instead of nitrogen such that0.1≦δ≦1; and p=0. In another embodiment, the oxygen is substituted byboth nitrogen and fluorine in a condition such that 0.1≦δ≦0.5 and0.05≦p≦0.3.

In one embodiment of the power transfer system with a BST materialsystem, oxygen is substituted by another anion such that z=0, and δ andp are both greater than 0. Thus in this embodiment, the anionsubstitutions are conducted in the absence of cation substitution. A BSTmaterial system with the composition Ba_(0.3)Sr₀₇TiO_(2.8)N_(0.13) ispresented as an example. The above-mentioned material shows an extremelylow dielectric loss of about 0.0001 with a suitable dielectric constantof about 506 at the frequency of about 2.5 MHz.

In one embodiment of the power transfer system, the BST material systemis doped with both cations and anions. In one embodiment, titanium ispartially replaced by chromium and oxygen is partially replaced bynitrogen such that z, δ and p are all greater than zero. In an example,a material with the compositionBa_(0.4)Sr_(0.6)Cr_(0.005)Ti_(0.995)O_(2.8)N_(0.13) is presented, whichdemonstrates a loss tangent of about 0.003 with a dielectric constant ofabout 819 at the frequency of about 3.13 MHz. In a further embodiment,0<x+y<1 and z, δ, and p are all greater than zero such that a cationicdopant is present in the barium or strontium site, chromium partiallysubstitutes titanium, and nitrogen partially substitutes oxygen. Table 3provides the dielectric values of some of the anion-doped materials inthe BST material system with and without cation dopants.

TABLE 3 Dielectric Loss BST material system Frequency constant tangentBa_(0.3)Sr_(0.7)TiO_(2.8)N_(0.13) ~1 MHz >500 ~0.005 ~2.5 MHz >500~0.00015 Ba_(0.3)Sr_(0.7)Cr_(0.005)Ti_(0.995)O_(2.8)N_(0.13) ~1 MHz >480~0.005 ~2.7 MHz ~470 ~0.0004 F doped Ba_(0.4)Sr_(0.6)TiO₃ 100 Hz- >400<0.01 prepared by using BaF₂ and SrF₂ 10 MHz as Ba and Sr sourcerespectively 1.49 MHz ~400 ~0.0001

As presented earlier, in one embodiment, a power transfer systemcomprising a field-focusing element 18 including a CCT material systemis presented such thatCa_(1-x-y)Ba_(x)Sr_(y)(Ca_(1-z)Cu_(z))Cu₂Ti_(4-δ)Al_(δ)O_(12-0.5δ),wherein 0≦x<0.5, 0≦y<0.5, 0≦z≦1, and 0≦δ≦0.1. In one embodiment, the CCTmaterial system comprises CaCu₃Ti₄O₁₂. In another embodiment, the CCTmaterial system comprises Ca₂Cu₂Ti₄O₁₂ having a dielectric constantgreater than about 3500 and a loss tangent less than about 0.07 at afrequency of about 100 kHz.

In one embodiment, in the power transfer system comprising a CCTmaterial system, x>0. In another embodiment, y>0. In one furtherembodiment, x>0 and y>0. Thus, in the above embodiments, calcium ispartially replaced by barium and/or strontium. One example of a CCTmaterial system prepared with barium and strontium dopants anddemonstrating very good dielectric properties isBa_(0.01)Sr_(0.2)Ca_(0.79)Cu₃Ti₄O₁₂. This material has a substantiallyuniform dielectric constant and loss tangent values over a wide range offrequency ranges, which makes this material useful for an applicationthat will work over a variable range of frequencies. The dielectricconstant for the material Ba_(0.01)Sr_(0.2)Ca_(0.79)Cu₃Ti₄O₁₂ lies inthe range of about 4500-5000 and the loss tangent is in the range ofabout 0.06 to 0.08 for the entire frequency range from about 1 kHz toabout 100 k Hz. The material is suitable for contactless powertransmission at any frequency lying in the range of about 1 kHz to 100kHz.

In one embodiment of the power transfer system comprising CCT materialsystem to be used in the field-focusing element 18, x and y are bothequal to zero and z=1, and the copper is partially replaced by othersuitable cations such as, for example, lanthanum. In one moreembodiment, the titanium is partially replaced by iron, aluminum,chromium, zirconium, or any of their combinations. In one embodiment,any or all of the above mentioned replacements coexist.

The examples presented below depict the different CCT material systemsthat can be used in the field-focusing element 18 presented above, alongwith their approximate measured dielectric constant and loss tangentvalues. While some particular examples are presented herein, thevariations in the dopant combinations and levels will be appreciated byone skilled in the art.

One example of a CCT material system exhibiting good dielectricproperties is CaCu₃Ti₄O₁₂. Table 4 lists some of the properties of thepure and doped CaCu₃Ti₄O₁₂ material.

TABLE 4 Dielectric Loss CCT material system Frequency constant tangentCaCu₃Ti₄O₁₂ 10 kHz-30 kHz >6000 <0.1CaCu_(2.9)La_(0.067)Ti_(3.94)Al_(0.06)O_(11.97) 10 kHz-60 kHz >6000 <0.1CaCu₃Ti_(3.94)Al_(0.06)O_(11.97) ~10 kHz >14000 ~0.11CaCu₃Ti_(3.99)Zr_(0.01)O₁₂ ~10 kHz >12000 <0.08CaCu_(2.9)La_(0.067)Ti_(3.98)Cr_(0.02)O_(11.99) ~10 kHz >12000 <0.2CaCu₃Ti_(3.98)Cr_(0.02)O_(11.99) 10 kHz-100 kHz >2000 <0.1

In one embodiment, in the CCT material system of the field-focusingelement 18 of the power transfer system, all of x, y, and z are equal tozero and the copper is partially replaced by other suitable cations suchas, for example, lanthanum. In one more embodiment, the titanium ispartially replaced by iron, aluminum, chromium, zirconium, or any oftheir combinations. In one embodiment, any or all of the above mentionedreplacements coexist.

The examples presented below depict the different embodiments presentedabove for a power transfer system with a field-focusing elementcomprising a CCT material system, along with the approximate measureddielectric constant and loss tangent values of the materials. While someparticular examples are presented herein, the variations in the dopantcombinations and levels will be appreciated by the one skilled in theart.

In one embodiment, Ca₂Cu₂Ti₄O₁₂ is a material in the CCT material systemof the field-focusing element 18 with about 33.3 mole % of CaCu₃Ti₄O₁₂and about 66.7 mole % of CaTiO₃. This material, in the pure form anddoped form exhibits some good dielectric properties as can be seen fromthe Table 5.

TABLE 5 Dielectric Loss CCT material system Frequency constant tangentCa₂Cu₂Ti₄O₁₂ ~100 kHz >3700 <0.07 Ca₂Cu₂Ti_(3.99)Zr_(0.01)O_(11.995) 100kHz-130 kHz >2000 <0.08 Ca₂Cu₂Ti_(3.94)Al_(0.06)O_(11.97) 3.5 kHz-10kHz >2000 <0.04 10 kHz-100 kHz >2000 <0.06 Ca₂Cu_(1.9)La_(0.067)Ti₄O₁₂100 kHz-130 kHz >1500 <0.09

In one embodiment of the power transfer system, the dielectric materialof the field-focusing element comprises SrTiO₃ along with the CCTmaterial system. One example of this dielectric material is (0.6CaCu₃Ti₄O₁₂+0.4 SrTiO₃). This combination has a dielectric constantvalue greater than about 7000 and the loss tangent value less than about0.09 at the frequency range from about 10 kHz to about 35 kHz. Anotherexample of this dielectric material is (0.6CaCu₃Ti_(3.94)Al_(0.06)O_(11.97)+0.4SrTiO₃). This combination has adielectric constant value greater than about 9000 and the loss tangentvalue less than about 0.09 at the frequency range from about 1 kHz toabout 10 kHz.

The inventors found that the density of materials also plays animportant role in the dielectric properties of the materials. If themicrostructure of the dielectric materials is dense, the materialscomprise fewer air pores in the material body. Air normally has a lowerdielectric constant than the dielectric materials and hence is expectedto lead to an overall lower dielectric constant, when present in thematerial. Therefore, the inventors conducted experiments to increaseoverall density of the materials and thereby increase the dielectricconstant. In one embodiment, different BST and CCT material systems weresintered at different high temperatures and were studied for theirdielectric constant and loss tangent values. It is found that thedielectric constant increased by increasing the sintering temperatures,while the loss tangent value decreased for the high temperature sinteredsamples. Further, it was observed that, both in the BST and CCTmaterials system, a high temperature sintering at lower sintering timehelped in reducing the loss tangent values compared to a lowertemperature sintering with larger sintering time. For example, a BSTmaterials system such as Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ sintered at1440° C. for 2 hours resulted in a material with lower loss tangentvalues compared to the same material sintered at 1350° C. for 12 hours.Similarly, a CCT material system sintered at 1100° C. for 2 hoursresulted in a material with lower loss tangent values compared to thesame material sintered at 1050° C. for 12 hours.

In one embodiment of the power transfer system, the BST and CCTmaterials intended to be used in a field-focusing element 18 were coldisostatically pressed (CIP) before sintering to increase the density ofmaterials. In one embodiment, the density of the BST materials obtainedby CIP and eventual sintering is greater than about 80% of thetheoretical density of those compositions. In one embodiment, thedensity is greater than about 90% of the theoretical density. In afurther embodiment, the density is greater than about 96% of thetheoretical density. In one more embodiment, the density is greater thanabout 98% of the theoretical density.

Example compositions processed by CIP includeBa_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ and Ba_(0.5)Sr_(0.4)Ca_(0.1)TiO₃.Comparison of dielectric constant values for some of the examplematerials between normally processed samples and samples that weresubjected to CIP are shown in Table 6, while Table 7 shows thecomparison of loss tangent values. From the tables, it can be seen thatwhile the increment in dielectric constant by subjecting the material toCIP prior to sintering was observed for all the materials at all thefrequencies, the effect of CIP in decreasing the loss tangent valueswere observed for comparatively higher frequency range measurements.

TABLE 6 BST material system 100 Hz 1 kHz 10 kHz 100 kHz 1 MHz 10 MHzBa_(0.5)Sr_(0.4)Ca_(0.1)TiO₃ (Normal) 2167.4 2096.5 2036.9 1994.6 1960.31948.8 Ba_(0.5)Sr_(0.4)Ca_(0.1)TiO₃ (CIP) 2855.9 2692.2 2623.2 2597.62581.1 4281.5 Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ (Normal) 381.3 164.5 1215.71190.6 1146.5 429.1 Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ (CIP) 3156.7 2491.72295.2 2238.2 2208.9 3101.5

TABLE 7 BST material system 100 Hz 1 kHz 10 kHz 100 kHz 1 MHz 10 MHzBa_(0.5)Sr_(0.4)Ca_(0.1)TiO₃ (Normal) 0.0282 0.0208 0.0170 0.0127 0.00860.0098 Ba_(0.5)Sr_(0.4)Ca_(0.1)TiO₃ (CIP) 0.0560 0.0299 0.0112 0.00550.0027 0.0995 Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ (Normal) 0.8883 8.64960.0422 0.0273 0.1237 2.8665 Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ (CIP) 0.25150.1169 0.0367 0.0144 0.0069 0.1617

However, all of the above-mentioned materials, by subjecting to CIP,showed very good dielectric constant values of greater than about 2000and low loss tangent values of less than about 0.08 in the frequencyranges of about 10 kHZ to about 2 MHz, such that the materials are goodfor using in a field-focusing element 18 for a contactless powertransfer application, along with being useful for other applications.

The inventors further conducted experiments on the dielectric materialsby treating the materials in different atmospheres such as anoxygen-rich atmosphere, a nitrogen atmosphere, or a reducing atmospheresuch as a hydrogen atmosphere, for example. An oxygen-rich atmosphere,for example, is able to effect changes in the dielectric properties ofCCT and BST family materials. It is observed that in the CCT familymaterials, sintering in the oxygen atmosphere compensates the oxygenvacancies in the materials, thus leading to lower dielectric constantand lower loss tangent. In the BST material system, sintering in theoxygen atmosphere increases the density of materials and thus increasesthe dielectric constant. Sintering in nitrogen atmosphere is expected totake out some of the oxygen from the materials, thus turning thematerial oxygen deficient, increasing the oxygen vacancies and electrondensities, and leading to high dielectric constant and increased losstangent. Tables 8 and 9 provide the dielectric constant and loss tangentvalues comparison respectively, for the example materialsBa_(0.5)Sr_(0.4)Ca_(0.1)TiO₃ and Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ at thefrequency range of about 100 Hz to about 1 MHz. Similar to the effect ofhigh temperature sintering, the oxygen atmosphere sintering in the BSTmaterials system was found to increase the dielectric constant, whilethe loss tangent values were also found to increase.

TABLE 8 BST material system 100 Hz 1 kHz 10 kHz 100 kHz 1 MHzBa_(0.5)Sr_(0.4)Ca_(0.1)TiO₃ (Normal) 2855.9 2692.2 2623.2 2597.6 2581.1Ba_(0.5)Sr_(0.4)Ca_(0.1)TiO₃ 3780.3 3261.1 3070.8 2979.9 2925.6 (O₂sintered) Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ 3156.7 2491.1 2295.2 2238.22208.9 (Normal) Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ 8071.6 4827.0 3648.13428.0 3368.3 (O₂ sintered)

TABLE 9 BST material system 100 Hz 1 kHz 10 kHz 100 kHz 1 MHzBa_(0.5)Sr_(0.4)Ca_(0.1)TiO₃ (Normal) 0.0560 0.0299 0.0112 0.0055 0.0027Ba_(0.5)Sr_(0.4)Ca_(0.1)TiO₃(O₂ sintered) 0.1800 0.0770 0.0290 0.01740.0080 Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃(Normal) 0.2515 0.1169 0.03670.0144 0.0069 Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃(O₂ sintered) 1.1900 0.43000.1400 0.0320 0.0100

In one experiment, BST materials were subjected to CIP and also weresintered in oxygen atmosphere for obtaining better dielectric values.Examples include, but not limited to, Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃sintered in oxygen atmosphere at about 1440° C. for 2 hours, leading toa dielectric constant value greater than about 1900 and loss tangentvalue less than about 0.01 in the frequency range of about 1 MHz toabout 10 MHz. Further, this material has a dielectric constant greaterthan about 1900 and a loss tangent value of about 0.0008 at thefrequency of about 2.91 MHz.Ba_(0.55)Sr_(0.4)Ca_(0.05)Cr_(0.01)Ti_(0.99)O₃ sintered in oxygenatmosphere at about 1440° C. for 2 hours has a dielectric constant valuegreater than about 1300 and the loss tangent value less than about 0.001in the frequency of about 4.95 kHz.

In one embodiment of the power transfer system, the dielectric materialsexist in the bulk material form and are polycrystalline, with grains andgrain boundaries. An increased grain boundary conduction in BST or CCTmaterial system may increase both dielectric constant and loss tangent.For example, a metallic precipitate at the grain boundary createselectrostatic potential due to the metal and electron interface, therebyincreasing grain boundary conduction and, consequently, the dielectricconstant and loss tangent.

In one embodiment of the power transfer system, any of the materialsdescribed above included in the field-focusing element is doped with abismuth-containing material, such as bismuth oxide. In a furtherembodiment, bismuth exists in a metallic phase in the grain boundariesof the polycrystalline materials used for field-focusing element. In arelated embodiment, bismuth oxide is doped and reduced to becomemetallic bismuth in the grain boundaries of the dielectric material. Inone embodiment, the bismuth oxide is introduced to the grain boundariesby mixing Bi₂O₃ and TiO₂ with the calcined BST powders before formingthe BST materials into the bulk form incorporable to the field-focusingelement 18 and sintering. In one embodiment, less than about 3 mole % ofBi₂O₃.3TiO₂ is present the BST material system. In one embodiment, theBST material system has a metallic bismuth phase in the grainboundaries. It is found that the dielectric constant of the BST materialsystem increases significantly by having a metallic bismuth phase in thegrain boundaries. In some instances, the increment in dielectricconstant value of the BST material system by disposing metallic bismuthin the grain boundary was more than about two orders of magnitude. Thematerial Ba_(0.4)Sr_(0.6)TiO₃ with 1 mole % Bi₂O₃.3TiO₂ doping can beconsidered as an example. This material demonstrates an extremely highdielectric constant, greater than about 30,800, with an extremely lowloss tangent factor of about 0.001 at a frequency of about 315 kHz, andtherefore is a good material for a field-focusing element of acontactless power transfer system as described herein.

In one experiment, BST material system was densified by cold isostaticpressing before sintering. In a further embodiment, the material wasalso doped with the bismuth oxide in the grain boundary and the bismuthoxide was reduced to metallic bismuth by reducing atmosphere treatmentsuch as 5% hydrogen in nitrogen at about 1200° C. for about 12 hours. Inone embodiment, a power transfer system comprising a field-focusingelement comprising a bismuth doped BST material system is presented. Theexamples include the materials such asBa_(0.4)Sr_(0.6)Cr_(0.01)Ti_(0.99)O₃+1 Mole % Bi₂O₃.3TiO₂ andBa_(0.4)Sr_(0.6)Cr_(0.01)Ti_(0.99)O₃+1 mole % Bi₂O₃.3TiO₂. Theabove-mentioned materials demonstrate extremely high dielectric constantof greater than about 11,030,000 at a frequency of about 100 Hz.However, the dielectric loss tangent of the materials have a somewhathigh value of about 0.9 at a frequency of about 100 Hz. These materialsmay be useful in applications where a high dielectric constant is ofhigh importance while the high loss tangent values can be accommodatedsuch as in low power transfer applications.

In one embodiment, power transfer system with a field-focusing elementcomprises a BST material system that is doped with both cations andgrain boundary dopants. Examples for the BST materials that had bothcation doping and grain boundary doping, and that show desirabledielectric properties, include Ba_(0.3)Sr_(0.7)Cr_(0.002)Ti_(0.998)O₃doped with about 1 mole % Bi₂O₃.3TiO₂. This material showed a dielectricconstant of about 7668 with a dielectric loss of about 0.007 at about1.4 MHz. While other applications can be envisaged, the above-mentionedmaterial is particularly suitable for the field-focusing element in thecontactless power transmission system for high power transfer describedherein. Another example of a dielectric material with both cation andgrain boundary doping is Ba_(0.3)Sr_(0.7)Cr_(0.005)Ti_(0.995)O₃ dopedwith about 1 mole % Bi₂O₃.3TiO₂. This material demonstrates a very highdielectric constant of greater than about 3,470,000 at the frequency ofabout 100 Hz. However, this material also has a high loss tangent valueof about 1 that may limit the application of the material in thefield-focusing element for high power transfer.

In one embodiment, a power transfer system with a field-focusing element18 comprises a BST material system material doped with both anions andgrain boundary dopants. In one embodiment, oxygen is partially replacedby nitrogen and bismuth was disposed in the grain boundaries. An exampleof a BST material that had both anion doping and grain boundary doping,and that showed desirable dielectric properties, includesBa_(0.3)Sr_(0.7)TiO_(2.8)N_(0.13) doped with about 1 mole % Bi₂O₃.3TiO₂.The above-mentioned material showed an extremely high dielectricconstant of about 1,793,610 at the frequency of about 100 Hz. However,this material had a loss tangent of about 1. This material can be usedfor low power transfer systems. Further, experimenting on differentsubstitution or methods for bringing down the loss tangent value mayresult in a more suitable material to be used in the field-focusingelement.

In one embodiment, a power transfer system with a field-focusing element18 comprises a BST material system material doped with cations, anions,and grain boundary dopants. In one embodiment, titanium is partiallyreplaced by chromium, oxygen is partially replaced by nitrogen, andmetallic bismuth is disposed in the grain boundaries. One example of amaterial having cation, anion, and grain boundary dopants in the BSTmaterial system is Ba_(0.3)Sr_(0.7)Cr_(0.005)Ti_(0.995)O_(2.8)N_(0.13)with about 1 mole % of Bi₂O₃.3TiO₂. This material showed an extremelyhigh dielectric constant greater than about 63,000 and dielectric losstangent of about 0.006 at a frequency of about 150 kHz. Therefore, thismaterial is very suitable for use in the field-focusing element in thepower transfer system described herein.

In one example, as described earlier in Table 3, the inventors variedthe starting materials for preparation of BST material system materialsand noted a decrease in the loss tangent. A Ba_(0.4)Sr_(0.6)TiO₃material was prepared by using BaF₂ and SrF₂ as the source of barium andstrontium respectively. By starting with the fluoride sources for bariumand strontium, it is expected that some of the fluorine will besubstituted for oxygen, thus changing the dielectric values of the BSTmaterials system. The Ba_(0.4)Sr_(0.6)TiO₃ prepared by using BaF₂ andSrF₂ showed a dielectric loss factor less than about 0.01 over theentire frequency range from 100 Hz to 10 MHz with a minimum of 0.0001 at1.4 MHz. The material also showed a uniform dielectric constant of about415 over the entire frequency range mentioned above. The material may beadvantageously used for transmitting contactless power at any frequencyrange from about 100 Hz to about 10 MHz.

In one embodiment of the power transfer system, it is desirable toemploy dielectric materials whose dielectric properties such asdielectric constant and loss tangent are stable over a certaintemperature range around room temperature to accommodate the changes intemperature due to, for example, environmental or operational changes.In one embodiment, the dielectric materials are beneficial if theirdielectric properties are substantially stable from about −50° C. toabout 150° C. “Substantially stable” as used herein indicates that thedielectric properties of the materials do not change more than about 10%of their room temperature values over a given temperature range. In oneembodiment, the dielectric materials presented herein are having theirdielectric properties substantially stable from about −15° C. to about120° C. In a further embodiment, the dielectric materials havedielectric properties that are substantially stable from about −20° C.to about 60° C. In one embodiment, the BST and CCT materials presentedhere are ceramic materials stable over a wide temperature range andhaving dielectric properties that are stable around room temperatures.

EXAMPLES

The following examples illustrate methods, materials and results, inaccordance with specific embodiments, and as such should not beconstrued as imposing limitations upon the claims. All components arecommercially available from common chemical suppliers.

Preparation of Materials:

A general method of preparation followed for the BST and CCT materialsystems identified in different examples are outlined below. However,one skilled in the art would appreciate that small variations in thestarting materials; temperatures, times, and atmospheres of preparation,calcination, and sintering; size and shape variations of the preparedpowders and bulk materials could be accommodated to the examplespresented below.

Preparation of Pure and Doped CCT and BST Material Systems

Stoichiometric concentrations of CaCO₃, CuO and TiO₂ were mixed andball-milled in dry conditions and calcined at 1000° C. for 24 hours inair. The calcination temperatures and atmospheres were varied for somematerials to investigate the effect of temperatures and atmospheres.BaCO₃, SrCO₃, Cr₂O₃, Al₂O₃, La₂O₃, Fe₂O₃, ZrO₂ were added in therequired mole percents by solid state mixing for doping barium,strontium, chromium, aluminum, lanthanum, iron, and zirconium dopantsrespectively, whenever required. About 1 mole % of Bi₂O₃.3TiO₂ was addedfor grain boundary doping. Urea was used for nitrogen doping in oxygensites by solid state mixing and calcining. Stoichiometric amounts ofBaF₂, SrF₂, and/or CaF₂ were used as starting materials for including afluorine dopant in the oxygen site.

The calcined mixture was added with about 2 wt % polyvinyl actetae (PVA)and mixed thoroughly using an agate mortar. The mixture was furthermilled using ball milling in isopropanol medium. The powders werepressed into green pellets using hydraulic pressing with a pressure of 4MPa followed by 6 MPa. For obtaining cold isostatic pressed (CIP)pellets, a CIP machine was used to further densify the hydrostaticallypressed pellets. The pellets were then sintered at 1050° C., 1100° C.,1350° C., or 1440° C. for 2, 12, or 24 hours in air, oxygen, or nitrogenatmosphere, as required. 5% hydrogen in nitrogen atmosphere was used forreducing bismuth oxide to metallic bismuth during sintering. Thesintered pellets were coated with silver paste for the purpose ofdielectric measurement. The dielectric measurements were carried outusing an Agilent 4294A impedance analyzer and verified using aNovocontrol Alpha-K impedance analyzer. XRDs of the calcined andsintered samples were verified. While the general method for thepreparation, processing and dielectric value measurements of materialsare outlined above, the examples provided below contain the specificdetails of preparation, processing, measurements, and results of some ofthe selected materials.

Example 1 Ba_(0.55)Sr_(0.4)Ca_(0.05)TiO₃ Processed by CIP

About 13.071 gm of BaCO₃, 9.579 gm of TiO₂, 10.152 gm of Sr(NO₃)₂ and0.6 gm of CaCO₃ were added together and hand mixed using mortar andpestle for 15 minutes. The mixture was added with approximately equalvolume of isopropanol and about 3 times by volume of zirconia grindingmedia and rack-milled for around 6 hours. The homogeneous mixture wastransferred to an alumina crucible and calcined at 1100° C. for 2 hrs.About 2 wt % of PVA was added and mixed to the calcined powder using anagate mortar. Equal volume of isopropanol was added to the resultantmaterial and rack-milled again.

The powder was then pressed into pellets of about 3 gram weight usinghydraulic pressing with a pressure of about 4 MPa. The pellets werevacuum sealed in polyethylene film and cold isostatically pressed withabout 30 MPa pressure. The pellets were sintered at 1440° C. for 2 hoursin air. A silver paste coating of a few microns thickness was applied tothe sintered pellets and was dried at 200° C. for 2 hours. Thedielectric constant and loss tangent of the pellet was then measuredusing Agilent 4294A impedance analyzer. Table 10 presents the dielectricmeasurement results of this material.

TABLE 10 Frequency Dielectric constant Loss tangent 100 Hz 3156.7 0.25151 kHz 2491.1 0.1169 10 kHz 2295.2 0.0367 100 kHz 2238.2 0.0144 1 MHz2208.9 0.0069 2.01 MHz 2218.8 0.001 10 MHz 3101.5 0.1617

Example 2 Ba_(0.01)Sr_(0.2)Ca_(0.79)Cu₃Ti₄O₁₂

About 0.079 gm of BaCO₃, 12.790 gm of TiO₂, 1.175 gm of SrCO₃, 3.165 gmof CaCO₃ and 9.554 gm of CuO were added together and hand mixed usingmortar and pestle for 15 minutes. The mixture was added withapproximately equal volume of isopropanol and about 3 times by volume ofzirconia grinding media and rack-milled for around 6 hours. Thehomogeneous mixture was transferred to an alumina crucible and calcinedat 1000° C. for 24 hrs. About 2 wt % of PVA was added and mixed to thecalcined powder using an agate mortar. Equal volume of isopropanol wasadded to the resultant material and rack-milled again.

The powder was then pressed into pellets of about 3 gram weight usinghydraulic pressing with a pressure of about 6 MPa. The pellets weresintered at 1100° C. for 2 hours in air. A silver paste coating of a fewmicrons thickness was applied to the sintered pellets and was dried at200° C. for 2 hours. The dielectric constant and loss tangent of thepellet was then measured using Agilent 4294A impedance analyzer. Table22 presents the dielectric measurement results of this material.

TABLE 11 Frequency Dielectric constant Loss tangent 1 kHz 5345.2 0.06910 kHz 4864.5 0.0634 34 kHz 4672.2 0.0604 100 kHz 4528 0.0794 1 MHz3638.8 0.3972 10 MHz 3638.8 2.904

Example 3 Ca₂Cu₂Ti_(3.94)Al_(0.06)O_(11.97)

About 8.497 CaCO₃, 6.753 gm of CuO, 13.357 gm of TiO₂ and 0.955 gm ofAl(NO₃)₃.9H₂O were added together and hand mixed using mortar and pestlefor 15 minutes. The mixture was added with approximately equal volume ofisopropanol and about 3 times by volume of zirconia grinding media andrack-milled for around 6 hours. The homogeneous mixture was transferredto an alumina crucible and calcined at 1000° C. for 24 hrs. About 2 wt %of PVA was added and mixed to the calcined powder using an agate mortar.Equal volume of isopropanol was added to the resultant material andrack-milled again.

The powder was then pressed into pellets of about 3 gram weight usinghydraulic pressing with a pressure of about 6 MPa. The pellets weresintered at 1100° C. for 2 hours in air. A silver paste coating of a fewmicrons thickness was applied to the sintered pellets and was dried at200° C. for 2 hours. The dielectric constant and loss tangent of thepellet was then measured using Agilent 4294A impedance analyzer. Table12 presents the dielectric measurement results of this material.

TABLE 12 Frequency Dielectric constant Loss tangent 3.41 kHz 2354.40.021 3.83 kHz 2344.4 0.0173 10 kHz 2303.1 0.0353 100 kHz 2203.7 0.06121 MHz 1948.4 0.349 10 MHz 706.7 1.16

Advantageously, power transfer systems as disclosed in certainembodiments herein are configured to include field-focusing elements andare less sensitive to the variations in the load as the frequency ofresonance. As described herein, field-focusing element 18 may be usedfor enhancing magnetic field focus and efficiency of the contactlesspower transfer system. Further, the field-focusing element comprises adielectric material that includes a BST material system, a CCT materialsystem or a combination of both. Use of the dielectric materialsincreases the magnetic field-focusing of the field-focusing element suchthat power and data transmission can be achieved simultaneously acrossthe primary coil, field-focusing element, and secondary coil.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A power transfer system comprising: a field-focusing elementcomprising a dielectric material, wherein the dielectric materialcomprisesCa_(1-x-y)Ba_(x)Sr_(y)(Ca_(1-z)Cu_(z))Cu₂Ti_(4-δ)Al_(δ)O_(12-0.5δ),wherein 0≦x, y<0.5; 0≦z≦1; and 0≦δ≦0.1.
 2. The system of claim 1,wherein at least one of x and y is greater than 0 when δ=0.
 3. Thesystem of claim 1, wherein x and y are both greater than 0 when δ=0. 4.The system of claim 3, wherein x and y are both greater than 0 and z=1when δ=0.
 5. The system of claim 4, wherein the dielectric materialcomprises Ba_(0.01)Sr_(0.2)Ca_(0.79)Cu₃Ti₄O₁₂.
 6. The system of claim 1,wherein x, y, and z are all equal to 0 and δ>0.
 7. The system of claim6, wherein the dielectric material comprisesCa₂Cu₂Ti_(3.94)Al_(0.06)O_(11.97).
 8. The system of claim 1, whereinx+y≦0.3.
 9. The system of claim 1, wherein δ≦0.6.
 10. The system ofclaim 1, wherein the dielectric material further comprises zirconium.11. The system of claim 10, wherein the dielectric material comprisesCa₂Cu₂Ti_(3.99)Zr_(0.01)O₁₂.
 12. The system of claim 1, wherein thedielectric material further comprises lanthanum.
 13. The system of claim1, wherein the dielectric material is a polycrystalline materialcomprising grains and grain boundaries.
 14. The system of the claim 1,wherein the system further comprises a first coil coupled to a powersource and spaced apart from the field-focusing element.
 15. The systemof the claim 14, wherein the system further comprises a second coilcoupled to a load and spaced apart from the field-focusing element. 16.The system of the claim 15, wherein the field-focusing element isdisposed between the first coil and second coil.
 17. A power transfersystem comprising: a first coil coupled to a power source; a second coilcoupled to a load; and a field-focusing element disposed between thefirst coil and the second coil and comprising a dielectric material,wherein the dielectric material comprisesCa_(1-x-y)Ba_(x)Sr_(y)Cu₃Ti₄O₁₂, wherein 0<x<0.2 and 0<y<0.2.
 18. Thepower transfer system of claim 17, wherein the field-focusing elementcomprises a plurality of resonators.
 19. A power transfer systemcomprising: a first coil coupled to a power source; a second coilcoupled to a load; and a field-focusing element disposed between thefirst coil and the second coil and comprising a dielectric material,wherein the dielectric material comprisesCa_(2-x-y)Ba_(x)Sr_(y)Cu₂Ti_(4-δ)Al_(δ)O_(12-0.5δ), wherein 0≦x<0.2;0≦y<0.2; and 0<δ≦0.1.
 20. The power transfer system of claim 19, whereinthe field-focusing element comprises a plurality of resonators.